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# Acids and Bases

A base is a compound that can donate an electron pair, while an acid is a compound that can accept an electron pair. Thus, an acid-base reaction would be a reaction where a base donates an electron pair to an acid. Although this is the modern definition, the classical definition is still more useful conceptually: an acid is a proton (H+) donor, while a base is a hydroxide (OH-) donor. By viewing it in this light, direct calculations of acidity can be done by measuring the concentration of protons within a solution. This measurement is known as the power of hydrogen, or pH: pH = -log([H+]) Example 1: So, if [H+] = 10^-2, then the pH = -log(10^-2) = 2 Basicity on the other hand can be calculated by measuring the concentration of the hydroxide ion: pOH = -log([OH-]) Example 2: So, if [OH-] = 10^-12, then the pOH = -log(10^-12) = 12 By looking at the dissociation constant of water, pH and pOH are intricately linked by the following relationship: Kw = 10^-14 = [H+]*[OH-] Taking the –log of both sides: 14 = -log([H+]) + - log([OH-]) 14 = pH + pOH Using this relationship, we can see that the pHs of both of the above examples are exactly the same: Example 1: pH = 2 Example 2: pH = 14 - pOH = 14-12 =2 Thus, understanding the definition of an acid and a base as well as the intricate relationship between these two entities is crucial to understanding how to interpret acid-base reactions no matter how complex they may seem. © BrainMass Inc. brainmass.com December 7, 2019, 2:05 pm ad1c9bdddf

## Categories within Acids and Bases

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